1. Technical Field
The present invention relates to a weight inspecting apparatus for inspecting the weight of a resin product molded by injection molding.
2. Related Art
Generally, a resin product such as a connector housing attached to an end portion of a wire harness for a vehicle is molded by injection molding. In this case, insufficient injection of a resin material, which is called xe2x80x9ca short shot, xe2x80x9d sometimes occurs. The short shot, i.e., the insufficient injection of material, occurs in a case where the molten resin material has failed to spread in the entire mold cavity and the material has become insufficient due to the effects of the temperature condition, the pressurizing condition, and the like. Also, the short shot occurs when an air vent for allowing air inside the mold to escape during injection has become clogged. When the short shot occurs, an unfilled portion occurs in the resin product, and the product therefore becomes defective. Such defective products include various types ranging from those which are extremely close to nondefective products to those having large unfilled portions.
Incidentally, to totally eliminate defective resin products by eliminating the short shots is difficult with the structures and techniques of the present injection molding machines. Even if the injection molding machine is an excellent one, the short shots occur at a rate of once every several thousand to tens of thousands of molding operations.
In the light of these circumstances, inspection is conducted for inspecting whether the molded resin products are nondefective or defective. As a conventional inspection method, the resin products ejected from the injection molding machine are conveyed on a conveying belt, each of the resin products thus conveyed is allowed to drop and is placed on a receiving tray, and the receiving tray is then moved onto an electronic balance. To measure the weight of the resin product, after the weight of the receiving tray including the resin product is measured, the weight in which the weight of the receiving tray was subtracted from the measured value is set as the result of measurement of the resin product. Then, on the basis of the result of measurement by the electronic balance a determination is made as to whether the resin product is nondefective or defective.
If the result of determination is nondefective, only one of two lifting/lowering arms supporting both end portions of the receiving tray is raised, which in turn tilts the receiving tray, discharging the resin product into a nondefective-product collecting box. On the other hand, if the result of determination is defective, the receiving tray is tilted in the opposite direction to that of the above-described operation, discharging the resin product into a defective-product collecting box.
According to this inspection method, it would be possible to reduce the trouble of human visual inspection by a large number of inspectors. In other words, if the resin product has been determined to be defective, it suffices if the inspector checks only that product by visual inspection. Since the number of molded products which are determined to be defective is very small, the number of objects subject to visual inspection by inspectors is small, so that inspection is possible with less labor.
[Problems to be Solved]
With the conventional weight inspection apparatus, however, since a plurality of resin products ejected from the injection machine drop forcibly, there are cases where not all resin products can be accommodated on the receiving tray. In this case, since the total weight of the resin products in a smaller number is actually measured, there is a problem in that even if those resin products are nondefective, it is erroneously considered that a defective product due to a short shot or the like is included among them.
In addition, there have been cases where even if the receiving tray is tilted, some of the resin products still remain there. When the inventors of this application examined that trouble, it was found that the trouble is due to the fact that the resin products are charged with static electricity when the mold is opened. Namely, the force with which the resin products between themselves or the resin products and the receiving tray are attracted to each other occurs due to the static electricity with which the resin products are charged. Consequently, even if the receiving tray is tilted, the resin products sometimes fail to be discharged. In this case, if resin products which have been molded later are placed on the receiving tray in the state in which a resin product which has been molded earlier still remains on the receiving tray, the total weight of the resin products in a greater number is actually measured. Accordingly, there is a problem in that even if those resin products are nondefective, it is erroneously considered that a defective product due to the occurrence of burrs or the like is included among the products.
The invention has been devised in view of the above-described problems, and its object is to provide a weight inspecting apparatus which makes it possible to improve the inspection accuracy of the resin products.
[Means for Solving the Problems]
To solve the above-described problems, in the invention according to aspect 1, the gist lies in a weight inspecting apparatus in which a receiving member for placing thereon a plurality of resin products molded by injection molding is provided, the receiving member is movable between a receiving position for receiving the resin products at a position spaced apart from a weight measuring instrument and a measuring position for measuring the weight of the resin products on the weight measuring instrument, and inspection is performed as to whether or not the resin products are nondefective on the basis of whether or not the total weight of the plurality of resin products placed on the receiving member at the measuring position is greater than a first upper-limit threshold, the weight inspecting apparatus comprising: storage means for storing a second upper-limit threshold which is yet greater than the first upper-limit threshold; and determining means for determining whether or not the total weight of the resin products is greater than the second upper-limit threshold when the total weight of the resin products is greater than the first upper-limit threshold.
In the invention according to aspect 2, the gist lies in a weight inspecting apparatus in which a receiving member for placing thereon a plurality of resin products molded by injection molding is provided, the receiving member is movable between a receiving position for receiving the resin products at a position spaced apart from a weight measuring instrument and a measuring position for measuring the weight of the resin products on the weight measuring instrument, and inspection is performed as to whether or not the resin products are nondefective on the basis of whether or not the total weight of the plurality of resin products placed on the receiving member at the measuring position is less than a first lower-limit threshold, the weight inspecting apparatus comprising: storage means for storing a second lower-limit threshold which is yet smaller than the first lower-limit threshold; and determining means for determining whether or not the total weight of the resin products is less than the second lower-limit threshold when the total weight of the resin products is less than the first lower-limit threshold.
In the invention according to aspect 3, the gist lies in a weight inspecting apparatus in which a receiving member for placing thereon a plurality of resin products molded by injection molding is provided, the receiving member is movable between a receiving position for receiving the resin products at a position spaced apart from a weight measuring instrument and a measuring position for measuring the weight of the resin products on the weight measuring instrument, and inspection is performed as to whether or not the resin products are nondefective on the basis of whether or not the total weight of the plurality of resin products placed on the receiving member at the measuring position is between a first upper-limit threshold and a first lower-limit threshold, the weight inspecting apparatus comprising: storage means for storing a second upper-limit threshold which is yet greater than the first upper-limit threshold and a second lower-limit threshold which is yet less than the first lower-limit threshold; and determining means for determining whether or not the total weight of the resin products is greater than the second upper-limit threshold when the total weight of the resin products is greater than the first upper-limit threshold, and determining whether or not the total weight of the resin products is less than the second lower-limit threshold when the total weight of the resin products is less than the first lower-limit threshold.
Hereafter, a description will be given of the xe2x80x9coperationxe2x80x9d of the invention.
In accordance with the invention according to aspect 1, a second upper-limit threshold which is yet greater than the first upper-limit threshold is set. Accordingly, when the total weight of the resin products is greater than the first upper-limit threshold as a result of the inspection of the resin products, and at least one of the resin products is thus found to be defective, a determination is further made as to whether or not the total weight of the resin products is greater than the second upper-limit threshold. For this reason, it is possible to specify due to what causes the resin products have become defective depending on whether or not the second upper-limit threshold has been exceeded. Hence, it is possible to improve the inspection accuracy of the resin products.
In accordance with the invention according to aspect 2, a second lower-limit threshold which is yet smaller than the first lower-limit threshold is set. Accordingly, when the total weight of the resin products is less than the first lower-limit threshold as a result of the inspection of the resin products, and at least one of the resin products is thus found to be defective, a determination is further made as to whether or not the total weight of the resin products is less than the second lower-limit threshold. For this reason, it is possible to specify due to what causes the resin products have become defective depending on whether or not the total weight of the resin products is less than the second lower-limit threshold. Hence, it is possible to improve the inspection accuracy of the resin products.
In accordance with the invention according to aspect 3, as has been described concerning the above-described operation in accordance with aspects 1 and 2, a determination is made as to whether or not the total weight of the resin products is greater than the second upper-limit threshold, and a determination is made as to whether or not the total weight of the resin products is less than the second lower-limit threshold. Accordingly, it is possible to further improve the inspection accuracy of the resin products.